The synthesis of 2-hydroxy alkyl carbamates from cyclic carbonates and ammonia or primary amines is well known to those skilled in the art. U.S. Pat. No. 5,912,382 discloses a process for the preparation of 2-hydroxy alkyl carbamates from either propylene carbonate or butylene carbonate and ammonia using an active hydroxyl compound as an initiator for the reaction.
No prior art can be found for 2-hydroxy alkyl carbamates containing unsaturated side chains.
Carbamate functional polymers and oligomers and methods to prepare carbamate functional materials are disclosed in the literature in numerous patents.
In U.S. Pat. No. 5,336,566, carbamate functional oligomers are described which are prepared from the reaction of hydroxy propyl carbamate and a triisocyanaurate of isophorone diisocyanate. A coating was prepared by crosslinking this oligomer with an aminoplast resin. This reference discloses that carbamate functional oligomers or polymers can be prepared from the reaction of any hydroxy carbamate with an oligomer or polymer containing isocyanate groups. The synthetic route to the hydroxy carbamate is not disclosed. The drawing included in the patent indicates that the synthetic route taken results in 1,3-hydroxypropyl carbamate. Also, while the possible use of other carbamates, such as hydroxy butyl carbamate, is mentioned, the effect of changing the structure of the carbamate on the properties of the oligomer or the coating is not disclosed.
U.S. Pat. Nos. 5,300,328; 5,356,669; 5,474,811; 5,605,965; 5,726,246 and EP 594,142 disclose the preparation of a carbamate functional polymer from the reaction of hydroxy propyl carbamate with an isocyanate functional polymer.
U.S. Pat. Nos. 5,373,069; 5,512,639 and 5,719,237 disclose the preparation of a carbamate functional oligomer from the reaction of hydroxy propyl carbamate and a difunctional isocyanate or the adduct of a difunctional isocyanate with a polyol.
U.S. Pat. Nos. 5,792,810 and EP 767,231 disclose the reaction of hydroxy propyl carbamate with caprolactone to form an adduct that retains both carbamate and hydroxyl functionality.
U.S. Pat. Nos. 5,792,810; 5,770,650; 5,760,127; and EP 869,139 and 767.187 disclose the preparation of carbamate functional polymer from the reaction of hydroxy propyl carbamate with caprolactone, followed by the reaction of the adduct with either a diisocyanate or adduct of a diisocyanate with a polyol. The use of caprolactone helps reduce the viscosity of the carbamate functional oligomer so that higher solids coatings can be prepared.
Several other patents disclose other methods of preparing oligomers or polymers with carbamate functionality. U.S. Pat. No. 5,766,769 discloses reacting hydroxy propyl carbamate with the cyclic siloxane, tetramethyl cyclotetrasiloxane. U.S. Pat. No. 5,756,213 discloses reacting a hydroxy propyl carbamatexe2x80x94caprolactone adduct with a carbonate to prepare a difunctional carbamate functional oligomer. Similarly, EP 767,226 discloses reacting a hydroxy propyl carbamatexe2x80x94caprolactone adduct with urea to form a difunctional carbamate functional oligomer.
To provide a water reducible carbamate functional oligomer, EP 661,315 discloses the reaction of a trifunctional IPDI adduct with dimethylolproprionic adduct and hydroxy propyl carbamate.
Carbamate functional oligomers are disclosed which are the reaction product of a hydroxy carbamate having pendant alkyl or vinyl groups and an oligomer or polymer containing at least one isocyanate group.
Hydroxy carbamates useful in this invention are most conveniently prepared from the reaction of a cyclic carbonate and either ammonia or a primary amine. Thus, ammonia can be reacted with ethylene carbonate to form hydroxy ethyl carbamate. When ammonia is reacted with propylene carbonate, 2-hydroxy propyl carbamate ((methyl)-2-hydroxy ethyl carbamate) is formed.
In this invention, ammonia or a primary amine is reacted with a cyclic carbonate having a pendant alkyl group of greater than one carbon atom. Thus, ammonia can be reacted with butylene carbonate, pentylene carbonate, hexylene carbonate to yield 2-hydroxy ethyl carbamates having ethyl, propyl, and butyl pendant alkyl chains, respectively. In addition, cyclic carbonates containing unsaturated side chains can be used. Thus, 4-vinyl ethylene carbonate can be reacted with ammonia to afford (vinyl)-2-hydroxy ethyl carbamate.
The carbamate functional oligomers of this invention are prepared by reacting a hydroxy carbamate with any polymer or oligomer having groups that are reactive with the hydroxyl group and not the carbamate group.
More preferred are monomers, polymers or oligomers having isocyanate groups.
Typical isocyanate compounds that may be useful for this invention are diisocyanates such as toluene diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, methylene diphenyl diisocyanate [MDI], xcex1,xcex1,xcex1xe2x80x2,xcex1xe2x80x2-xylylene diisocyanate [TMXDI], and the like.
More preferred are oligomers prepared from the controlled polymerization or oligomerization of the difunctional isocyanates listed above. For example, oligomers of hexamethylene diisocyanate are sold under the tradename Desmodur by Bayer. The triisocyanarate of isophorone diisocyanate is sold as T1890 by Huls.
Also preferred are adducts made from reaction of a diisocyanate with a trifunctional alcohol. For example, three moles of a diisocyanate such as TMXDI can be reacted with one mole of trimethylol propane to yield an isocyanate functional oligomer.
Also useful for this invention are isocyanate functional polymers prepared from the free-radical polymerization of a vinyl monomer containing an isocyanate group. Such isocyanate functional vinyl monomers include m-isopropenyl-xcex1,xcex1-dimethyl benzyl isocyanate [m-TMI], isocyanatoethyl methacrylate, and the reaction product of a hydroxy functional vinyl monomer (such as hydroxy ethyl acrylate) with a diisocyanate.
The reaction of the hydroxy alkyl carbamate with the isocyanate functional oligomer or polymer may be conducted either in the presence or in absence of solvent. It is important that any solvent used not be reactive with the isocyanate. Solvents which can be used are toluene, xylene, esters such as butyl acetate, propylene glycol methyl ether acetate, EEP, ketones such as acetone methyl amyl ketone, and the like.
The reaction of the hydroxy alkyl carbamate with the isocyanate functional oligomer or polymer can also be conducted at ambient or elevated temperatures and, optionally, in the presence of a catalyst. Typical catalysts are those known in the art for catalyzing the reaction of an isocyanate with an alcohol. Preferred are tin compounds.
We have found that using hydroxy alkyl carbamates with pendant alkyl groups of greater than one carbon atom result in carbamate functional oligomers having lower solution viscosity than those with pendant alkyl chains with one or less carbon atoms. Considering the large amount of prior art in this area, the fact that using 2-hydroxy carbamates with pendant alkyl chains of greater than one carbon atom has not been disclosed as a way to reduce viscosity of the carbamate functional oligomer indicates that this invention is not obvious. Reducing the viscosity of carbamate functional oligomers is important in preparing higher solids coatings.
The carbamate functional polymer or oligomer is mixed with an aminoplast resin and optionally, pigments, flow control additives, rheology additives, catalysts, and solvents, to form a mixture that can be applied to a substrate and cured to form a coating. The aminoplast resin can be any etherified and alkylated resin derived from melamine or urea and formaldehyde.
In the following examples, several materials will be identified by abbreviations or trade names. These are identified as follows:
T1890-100 is a 100% solids version of the triisocyanaurate of isophorone diisocyanate from Huls.
PM acetate is the acetate of propylene glycol monomethyl ether.
DBTDL is dibutyl tin dilaurate.
Resimene 745 (R-745) is substantially hexamethoxy methyl melamine resin supplied by Solutia, Inc. (formerly Monsanto).
FC-430 is a fluorocarbon flow aid from 3M.
PTSA is p-toluene sulfonic acid.
The polymers and coatings are characterized using the following methods:
Fourier Transform Infrared Spectroscopy
Fourier Transform Infrared Spectroscopy is used to follow the reaction of the hydroxy carbamate with isocyanate. Samples were coated onto zinc selenide crystals and a FTIR spectrum measured.
Methyl Ethyl Ketone Resistance
Cured films were rubbed with a methyl ethyl ketone saturated cloth according to ASTM D-5402. Results are reported as the number of double rubs required for breakthrough of the film to the substrate. Test is terminated after 300 MEK double rubs. A rating of  greater than 300 indicates that the film was not marred.
Pencil Hardness
Pencil hardness was measured using a series of pencils containing leads of differing hardness according to ASTM D-3363. The hardness is reported as the hardest pencil lead that does not penetrate the coating film.
Konig Pendulum Hardness
The Konig pendulum hardness (KPH) is determined using a Byk-Gardner pendulum hardness tester according to ASTM D-4366. Hardness is reported as the number of seconds required for the pendulum swing to be damped from a 6xc2x0 swing to a 3xc2x0 swing.
Impact Resistance
Forward and reverse impact resistance is determined using a falling dart impact tester according to ASTM D-2794. Results are reported as the maximum in-lbs of force where the film remains intact.